Question

中考数学几道解答题

Answer 1

5.
延长AD并过B点作AC的平行线，相交于G点
则AC//BG,AE=EF,
可得BF=BG
在三角形BDG和三角形CDA中
BD=CD,<ADC=<GDB,<DBG=<ACD，
两三角形全等
所以AC=BG=BF6.★=x+y
1=y-x
2x-y=y-2x
解方程x=1
y=2
★=37.由XX-4X-(K-1)=0得出XX-4X+1=K
(1)
把(1)代入XX+KX-3=0得出
XX+X(XX-4X+1)-3=0
XX+XXX-4XX+X-3=0
XXX-3XX+X-3=0
(XXX+X)-3XX-3=0
X(XX+1)-3(XX+1)=0
(XX+1)(X-3)=0
因为XX只能等于或大于0.所XX+1不可能会等于0.所以X-3=0得出X=3
把X=3代入(1)得出K=9-12+1=-2
8.
(x-4)/(x-5)
-
(x-5)/(x-6)=(x-7)/(x-8)
-
(x-8)/(x-9)

1+1/(x-5)-1-1/(x-6)=1+1/(x-8)-1-1/(x-9)

1/(x-5)(x-6)=1/(x-8)(x-9)
x^2-11x+30=x^2-17x+72

6x=42
x=7
9.这题非常简单原理就是(1/2)*(1/3)=(1/2)-(1/3)=1/6所以原式=1/x-1/(x+2007)10.(1)a^2-3a-1=0,
a-3-1/a=0
a-1/a=3
(a+1/a)^2=(a-1/a)^2+4=13
a+1/a=±√13
a^2+1/a^2=(a-1/a)^2+2=11
当a+1/a=√13时
a^3+1/a^3
=(a+1/a)(a^2-1+1/a^2)
=√13*(11-1)
=10√13
当a+1/a=-√13时
a^3+1/a^3
=(a+1/a)(a^2-1+1/a^2)
=-√13*(11-1)
=-10√13
(2)a+1/a=3
a^2+1/a^2+2=9
a^2+1/a^2=7
a^4+1/a^4+2=49
a^4+1/a^4=47 (3).
A+1/A=2得A=1,所以A^N+1/A^N=1+1=2